Power management in a network of interconnected switches

ABSTRACT

A switch can reduce power consumption in a switch network by disabling under-utilized links between switches. The switch can include one or more line cards each operable to transmit and receive packets over a respective link to a remote switch. The switch can also comprise a control mechanism operable to place under-utilized links in standby mode whenever possible to conserve power. During operation, the switch can receive a standby request for placing a first link to a neighboring switch in a standby mode, and determines whether one or more eligible links to the neighboring switch can accommodate traffic from the first link. If the eligible links are able to accommodate traffic from the first link, and if the local switch and the neighboring switch agree to place the first link in standby mode, the local switch proceeds to place the first link in standby mode.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/099,974, Attorney Docket Number BRCD-3319.0.1.US.PSP, entitled “Power Saving Feature for ISLs in a Fabric,” by inventors Ram Kumar Gandhi, Shivalingayya Chikkamath, and Mythilikanth Raman, filed 5 Jan. 2015, the disclosures of which are incorporated by reference herein.

The present disclosure is related to U.S. patent application Ser. No. 13/087,239, (attorney docket number BRCD-3008.1.US.NP), entitled “Virtual Cluster Switching,” by inventors Suresh Vobbilisetty and Dilip Chatwani, filed 14 Apr. 2011, the disclosure of which is incorporated by reference herein.

BACKGROUND

1. Field

The present disclosure relates to network design. More specifically, the present disclosure relates to a method for a constructing a scalable switching system that facilitates automatically minimizing power consumption across the network switches.

2. Related Art

The relentless growth of the Internet has brought with it an insatiable demand for bandwidth. As a result, equipment vendors race to build larger, faster, and more versatile switches to move traffic. However, the size of a switch cannot grow infinitely. It is limited by physical space, power consumption, and design complexity, to name a few factors. More importantly, because an overly large system often does not provide economy of scale due to its complexity, simply increasing the size and throughput of a switch may prove economically unviable due to the increased per-port cost.

One way to increase the throughput of a switch system is to use switch stacking. In switch stacking, multiple smaller-scale, identical switches are interconnected in a special pattern to form a larger logical switch. However, switch stacking requires careful configuration of the ports and inter-switch links. The amount of required manual configuration becomes prohibitively complex and tedious when the stack reaches a certain size, which precludes switch stacking from being a practical option in building a large-scale switching system. Furthermore, a system based on stacked switches often has topology limitations which restrict the scalability of the system due to fabric bandwidth considerations.

Some switching technologies can manage individual links to optimize power usage. However, these technologies cannot be used in a switch system, because shutting down a link when traffic gets low may break the topology of the switch system.

SUMMARY

One embodiment provides a switch that facilitates reducing power consumption in a switch network by disabling under-utilized links between switches when other links can accommodate the leftover traffic. The switch can include one or more line cards each configured to transmit and receive packets over a respective link to a remote switch. The switch also includes a control mechanism operable to place under-utilized links in standby mode whenever possible to conserve power. During operation, the switch can receive a first standby request for placing a first link to a neighboring switch in a standby mode, and determines whether one or more eligible links to the neighboring switch can accommodate traffic from the first link. If the one or more eligible links are able to accommodate traffic from the first link, and if the local switch and the neighboring switch agree to place the first link in standby mode, the local switch proceeds to place the first link in standby mode.

In some embodiments, the one or more eligible links include links to the neighboring switch that do not have a pending standby request.

In some embodiments, the control mechanism can reject the first standby request in response to determining that the one or more eligible links cannot accommodate traffic from the first link.

In some embodiments, if the first standby request originated from a local line card, and the control mechanism can place the first link in standby mode by sending, to the neighboring switch, a second standby request for placing the first link in standby mode. The control mechanism rejects the first standby request in response to determining that the neighboring switch has not acknowledge the second standby request within a predetermined timeout period.

In some embodiments, if the first standby request originated from a local line card, the control mechanism can place the first link in standby mode by determining that there exist other pending standby requests at the local routing bridge, and determining whether the one or more eligible links to the neighboring switch can accommodate traffic from the first standby request and all other pending standby requests. The control mechanism can reject the first standby request in response to determining that the eligible links cannot accommodate traffic from the first standby request and all other pending standby requests.

In some embodiments, if the standby request originated from the neighboring switch, the control mechanism determines whether there exist any pending standby requests from a local line card. If a pending standby request from a local line card exists, the control mechanism defers processing of the standby request from the neighboring switch until there are no pending standby requests from any local line cards.

In some embodiments, the control mechanism determines whether a priority is sufficiently high among the eligible links that are to accommodate traffic for the first link. If the priority among the eligible links is not sufficiently high, the control mechanism rejects the first standby request.

In some embodiments, the control mechanism determines whether the first link is a member of a trunk. If the first link belongs to a trunk, the control mechanism updates trunk state information to remove the first link from the trunk.

In some embodiments, the control mechanism can receive a link activate request from a line card. In response, the control mechanism selects, from a set of eligible links in standby mode, a link with a lowest priority that satisfies a priority requirement from the line card, and activates the selected link.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an exemplary switch network 100 in accordance with an embodiment.

FIG. 2 presents a flow chart illustrating a method 200 for processing a standby request from a local line card in accordance with an embodiment.

FIG. 3 presents a flow chart illustrating a method for processing a standby request from a neighboring cluster in accordance with an embodiment.

FIG. 4 illustrates an exemplary switch network after placing links in standby mode in accordance with an embodiment.

FIG. 5 presents a flow chart illustrating a method for processing a link activate request to activate a link in standby mode in accordance with an embodiment.

FIG. 6 illustrates an exemplary switch that facilitates managing links in a switch network in accordance with an embodiment.

In the figures, like reference numerals refer to the same figure elements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Overview

Embodiments of the present invention provide a network of interconnected switches that solve the problem of reducing power consumption in the switch network by disabling under-utilized links between switches when other links can accommodate the leftover traffic. The switch network comprises a distributed set of switches, which are interconnected by Inter Switch Links (ISLs). The ISL links can be logical links, and carry the traffic between the switches of the switch network. The switches can perform distributed and dynamic provisioning of ISLs to conserve power across the individual switches.

For example, if an ISL link is not utilized or underutilized, the switch clusters at opposing ends of the ISL link can put the link in a standby mode, which reduces the power consumption of the line cards that drive the ISL link. During operation, the distributed switches can bring up or tear down the ISL link of the switch network as necessary to operate the active ISL links in as close to their maximum bandwidth as possible. This minimizes the number of ISL links operating at less than half their possible bandwidth, which consume more power than having less ISL links operating at near their maximum bandwidth.

The individual switch clusters or switches in the switch network can be an Ethernet switch, a routing bridge (RBridge), or a switch cluster. If multiple ISLs exist between two neighboring switches, these ISLs can automatically be combined to form a logical ISL trunk. Also, there can be multiple trunks between two switches, and each trunk can have multiple ISL links that carry traffic between the switches. During operation, the distributed switches can also bring up or tear down the ISL links of the switch network as necessary to add necessary bandwidth to a trunk, or to release underutilized bandwidth from the trunk. Hence, the switch network allows neighboring switches to reconfigure their trunks on-the-fly to ensure these trunks make optimal use the available ISL links, while minimizing the power consumption of the line cards that drive these ISL links.

It should be noted that a virtual cluster switch is not the same as conventional switch stacking. In switch stacking, multiple switches are interconnected at a common location (often within the same rack), based on a particular topology, and manually configured in a particular way. These stacked switches typically share a common address, e.g., IP address, so they can be addressed as a single switch externally. Furthermore, switch stacking requires a significant amount of manual configuration of the ports and inter-switch links. The need for manual configuration prohibits switch stacking from being a viable option in building a large-scale switching system. The topology restriction imposed by switch stacking also limits the number of switches that can be stacked. This is because it is very difficult, if not impossible, to design a stack topology that allows the overall switch bandwidth to scale adequately with the number of switch units.

In contrast, a switch network, or a network of interconnected switches (which can be referred to as a switch fabric, a virtual cluster switching (VCS) fabric, or simply as “VCS”) can include an arbitrary number of switches with individual addresses, can be based on an arbitrary topology, and does not require extensive manual configuration. The switches can reside in the same location, or be distributed over different locations. These features overcome the inherent limitations of switch stacking and make it possible to build a large “switch farm” which can be treated as a single, logical switch. Due to the automatic configuration capabilities of the switch fabric, an individual physical switch can dynamically join or leave the switch fabric without disrupting services to the rest of the network.

Furthermore, the automatic and dynamic configurability of switch fabric allows a network operator to build its switching system in a distributed and “pay-as-you-grow” fashion without sacrificing scalability. The switch fabric's ability to respond to changing network conditions makes it an ideal solution in a virtual computing environment, where network loads often change with time.

FIG. 1 illustrates an exemplary switch network 100 in accordance with an embodiment. Switch network 100 may include an Internet Protocol (IP) network, a Multiprotocol Label Switching (MPLS) network, a Transparent Interconnection of Lots of Links (TRILL) network, a Fibre Channel (FC) network, or may include any network technology now known or later developed. Specifically, switch network 100 can include a plurality of switch clusters, which are interconnected via Inter Switch Link (ISL) logical links. These ISL logical links are hereinafter referred to as ISL links, or simply as “links.”

In some embodiments, the ISL links can carry bidirectional traffic. Each switch can include multiple line cards, each of which includes a transmission (tx) circuit and a receiving (rx) circuit for sending and receiving data over a network link. A switch can use multiple line cards to establish and maintain multiple ISL links for interfacing with one or more other switches. For example, switch network 100 can include a switch 104 interconnected with a switch 104 via an ISL link 118, interconnected with a switch 108 via an ISL link 122, and interconnected with a switch 110 via an ISL link 120.

In some embodiments, multiple ISL links can be combined to form a high-bandwidth ISL trunk. The individual switches can add ISL links to a trunk when the trunk needs additional bandwidth, and can remove ISL links from the trunk when the trunk is underutilizing the ISL links in the trunk. For example, switch network 100 may include a switch 106 that can be interconnected with switch 104 via a trunk 112, made up of ISL links 124, 126, and 128. Moreover, switch 106 can be interconnected with switch 108 via two trunks: a trunk 114 comprising ISL links 130 and 132; and a trunk 116 comprising ISL links 134 and 136.

In some embodiments, each switch (or each switch of a switching cluster) can include software running on the switch, which manages a local state of each ISL link to which the switch is connected. When a line card of a switch detects that low traffic is running on an ISL link, the line card generates a standby request notification requesting to transition the ISL link into standby mode. The switch's software can receive standby request messages from the local line cards, and decides which ISL links are to enter standby mode and which ISL links are to remain operational. For example, the switch can calculate the total bandwidth crossing an ISL trunk made up of a plurality of ISL links. If the switch determines that the traffic can be accommodated into fewer ISL links than are currently active in the trunk, the switch selects one or more links to place in standby mode.

In some embodiments, each ISL link can have an associated low bandwidth threshold, and an associated high bandwidth threshold. During operation, if a line card monitoring traffic on an ISL link detects that the traffic drops below the low bandwidth threshold, the line card generates a standby request notification for the ISL link. On the other hand, if the line card detects that the ISL link's traffic is rising above the high bandwidth threshold, the line card generates an activate request message for the switch.

A user or administrator of a switch can preconfigure the low bandwidth and high bandwidth thresholds for the ISL links, as well as the Quality of Service (QoS) policies for the individual ISL links and ISL trunks. For example, if the user is concerned about the HTTP traffic in the switch network, the user can configure a policy that is specific to the HTTP traffic. Instead of setting the high and low bandwidth threshold values for all traffic across an ISL link, the user can set certain high and/or low bandwidth threshold values for the HTTP traffic. The user can also create other policies to set other bandwidth threshold values for other types of traffic.

In some embodiments, the individual switches can each implement a trunk state machine (TKSM) for each ISL trunk to which the switch is connected. This TKSM can include a current state for the links that make up ISL trunk 112, such as the set of member ISL links, and their recent bandwidth. For example, switches 104 and 106 can updates their local TKSM for ISL trunk 112 in response to adding a link to ISL trunk 112, or in response to removing a link from ISL trunk 112. If switches 104 and 106 agree to place ISL link 124 in standby mode due to low traffic across trunk 112, switches 104 and 106 will each update their local TKSM for trunk 112 to remove ISL link 124 from trunk 112.

Also, if switch 104 (or switch 106) re-activates ISL link 124 to increase the bandwidth across trunk 112, link 124 will first exist as an individual ISL link outside of ISL trunk 112. Once ISL link 124 is active, switches 104 and 106 can update their local TKSM for ISL trunk 112 to add ISL link 124 into ISL trunk 112. From this point forward, the entire traffic between switches 104 and 106 can be carried across the three ISL links of ISL trunk 112 (e.g., links 124, 126, and 128), based on the TKSM.

In some embodiments, a switch can store and manage multiple TKSMs. For example, switches 106 and 108 can transfer traffic to each other over two separate ISL trunks 114 and 116. Switches 106 and 108 may keep ISL trunks 114 and 116 separate when they each trunk requires different network parameters, or when each trunk has been been provisioned for different customers. Switches 106 and 108 can each store a TKSM for ISL trunk 114, and a separate TKSM for ISL trunk 116.

In exemplary switch network 100, the TKSM for ISL trunk 114 can be initially configured to include link status information for ISL links 130 and 132, and the TKSM for ISL trunk 116 can be initially configured to include link status information for ISL links 134 and 136. However, if switches 106 and 108 agree to place ISL link 132 in standby mode due to low traffic across at least one direction, ISL trunk 114 is left with only ISL link 130. At this point, both switches 106 and 108 may destroy the TKSM for ISL trunk 114, leaving ISL link 130 as a standalone link.

Moreover, it is possible for switches 106 and 108 to combine two or more ISL trunks into one ISL trunk if they have compatible link parameters. For example, switch 108 may analyze a set of parameters associated with ISL link 130 and the TKSM for ISL trunk 116 to determine whether they are compatible. If the link parameters for ISL link 130 do not contradict the link parameters for ISL trunk 116, switches 106 and 108 can add ISL link 130 to ISL trunk 116, and also update their TKSM for ISL trunk 116 to include ISL link 130 as a member link. However, if the link parameters for ISL link 130 are not compatible with those of ISL trunk 116, switches 106 and 108 will leave ISL link 130 as a standalone link.

In some embodiments, when ISL link 132 is placed in standby mode, it becomes available to expand the bandwidth capacity for ISL trunk 116 or ISL link 130 in the future. For example, if transmission traffic from switch 108 increases above a maximum bandwidth threshold for ISL link 134 or 136, switch 108 can activate ISL link 132. However, in order to offload traffic from ISL trunk 116 onto ISL link 132, switch 108 needs to change the configuration parameters for ISL link 132 to match those of ISL trunk 116, and can add ISL link 132 to ISL trunk 116 by updating the TKSM to include ISL link 132 as a member link of ISL trunk 116. At this point, switch 108 can transmit traffic for ISL trunk 116 via ISL link 132 in addition to ISL links 134 and 136.

Placing Links in Standby Mode

In some embodiments, each line card can include an HSL software module running in the line card. The HSL module can include a kernel module, running at the hardware subsystem layer to monitor the network traffic for the corresponding line card's physical link. More specifically, the HSL modules of the switch network can run as a synchronized distributed system across each of the line cards in the switch network. Each HSL module instance maintains the global topology information all ISL links and ISL trunks of the switch network, and synchronizes changes to the switch network topology information with other HSL module instances of other switches via the active ISL links and trunks. This ensures that the individual HSL module instances of the switch network have a common view of the switch network's topology, which makes it possible for them to use their local network topology information when deciding which ISL links to place in standby mode or to activate.

For example, switches 102 and 104 are interconnected by a single ISL link 118. If the traffic across ISL link 118 drops to below the low bandwidth threshold, the HSL modules for ISL link 118 at switches 102 and 104 would generate a standby request notification for switches 102 and 104, respectively. However, bringing down ISL link 118 would disconnect a portion of the switch network (namely, the link between switches 102 and 104) because there are no other links that can carry the traffic that would no longer be carried by ISL link 118. Because of this, switches 102 and 104 will not honor the standby request for ISL link 118.

As another example, assume that the traffic for ISL link 124 drops below a minimum threshold. In response to detecting this low traffic, the HSL module for ISL link 124 at switch 104 can issue a standby request. If ISL links 126 and 128 can accommodate the traffic from ISL link 124, switch 104 can send a standby request message to its neighboring switch across ISL link 124 (e.g., to switch 106). Switch 106 then either acknowledges that ISL link 124 can be placed in standby mode, or can deny the request to place ISL link 124 in standby mode. If switch 106 returns an acknowledgement message, then both switches 104 and 106 may proceed to place ISL link 124 into standby mode. Switch 104 then places ISL link 124 in standby mode by returning an acknowledge message to the local HSL module for ISL link 124, which in turn disables the transmit and receive radios for ISL link 124.

However, if ISL links 126 and 128 cannot accommodate the traffic, or if switch 106 does not acknowledge the standby request (e.g., by returning a negative acknowledgement (NACK) message to deny the standby request, or by not returning an ACK message within a timeout period), then switches 104 and 106 will keep ISL link 124 active.

In some embodiments, placing an ISL link in standby mode is a two-level process. Initially, a line card for the ISL link generates a standby request for the ISL link when the ISL link's bandwidth drops below a low bandwidth threshold. A software module running on the switch that carries the line card receives the standby request from the line card, and processes the line card's standby request to determine whether the local switch can place the ISL link on standby. The switch's software module stores global network topology information, the ISL trunk state machines, and the QoS priority information, and uses this information to determine whether to place the ISL link on standby.

Then, if the local switch can place the ISL link on standby, the software module proceeds to issue another standby request to the neighboring switch at the other side of the ISL link. The two switches place the ISL link on standby if they are in agreement to do so.

FIG. 2 presents a flow chart illustrating a method 200 for processing a standby request from a local line card in accordance with an embodiment. During operation, the switch can determine whether a line card has issued a new standby request (operation 202). Note that it's possible that the switch may receive a standby request from a line card while the switch is awaiting a standby acknowledgement from a neighboring switch for another ISL link. However, it's likely that the traffic bandwidth that needs to be accommodated after placing both ISL links in standby mode may be more than what the remaining eligible ISL links can handle.

In some embodiments, if the switch has received a new standby request from a line card (operation 202), the switch determines whether the eligible links can accommodate traffic from links associated with the standby request and all other pending standby requests (operation 204). Hence, during operation 204, the switch determines an aggregate bandwidth for the requesting ISL link and the other pending standby requests, and determines whether one or more active ISL links or trunks have sufficient available bandwidth to accommodate this aggregate bandwidth without causing any of the ISL links or trunks to surpass a high bandwidth threshold.

If the remaining ISL links cannot accommodate the aggregate traffic, the switch will discard the new standby request from the line card (operation 206), and may preserve the other pending standby requests that have already been confirmed to be offloadable to other ISL links. For example, the new standby request may be for an ISL link that is meant to carry at least some of the traffic being offloaded by the other ISL links with pending standby requests. Hence, by discarding the recent standby request, the switch is ensuring that there is sufficient bandwidth available to for the ISL links associated with the other pending standby requests.

In some embodiments, if the local switch has received standby requests from another switch on a neighboring switch before or while processing the standby request from the local line card, the switch places the standby request from the neighboring switch on hold until the local switch has processed all standby requests from the local line cards.

On the other hand, if the remaining eligible links can accommodate the aggregate traffic for the switch (operation 204), the switch performs a Quality of Service (QoS) priority check among the eligible ISL links to determine whether the QoS priority is sufficiently high among the eligible links to satisfy the QoS priority requirements of the aggregate traffic (operation 208). If the QoS priority check does not succeed, the switch discards the standby request (operation 206).

Otherwise, the switch sends a standby request for placing the requesting ISL link in standby to a neighboring switch at the other end of the ISL link (operation 210), and waits for an acknowledgement (ACK) message from the neighboring switch for a predetermined timeout period (operation 212). If the switch receives the acknowledgement message within the timeout period (operation 214), the HSL module proceeds to place the ISL link associated with the new request in standby mode (operation 216). The switch may also inform local software modules that the ISL link is offline.

Otherwise, if the switch does not receive the in time or receives a negative acknowledgement message (NACK) rejecting the standby request, the switch proceeds to discard the new standby request (operation 206).

When the neighboring switch receives the standby request over the ISL link, the neighboring switch analyzes its outbound traffic across the ISL link to determine whether other ISL links can accommodate its outbound traffic. If so, the neighboring switch returns an acknowledgement message, which informs the local line card's HSL module that the ISL link can be placed in standby mode. At this point, both the local HSL module and an HSL module at the neighboring switch can proceed to place their transmit and receive circuits for the ISL link in standby mode. Also, if the ISL link is a member of an ISL trunk, both the local switch and the neighboring switch will update their trunk state machine (TKSM) to remove the ISL link from the trunk.

On the other hand, if the neighboring switch cannot accommodate the ISL link's traffic across other ISL eligible links or trunks (e.g., ISL links that are not pending to be placed in standby), the neighboring switch will reject the standby request. The neighboring switch may not return an acknowledgement message, or may return a NACK message to reject the standby request. For example, in some embodiments, it's possible that the local switch and the neighboring switch may issue two different standby requests to each other, such that there may not be enough eligible ISL links to support the additional bandwidth leftover after placing the two ISL links in standby.

For example, referring to switch network 100 of FIG. 1, switch 104 may issue a standby request to place ISL link 124 in standby mode when switch 104 can move its own outbound traffic for ISL link 124 over ISL links 126 and 128. At the same time, switch 106 may issue a standby request to place ISL link 126 in standby mode, prior to receiving the standby request for ISL link 124. At this point, switch 106 determines that eligible ISL links 124 and 128 can accommodate the traffic for ISL link 126, which are active at switch 106 and not currently pending a standby request at switch 106.

Then, after having sent the standby request for ISL link 126, switch 106 receives the standby request for ISL link 124 and determines whether ISL link 124 can be placed in standby mode in addition to disabling all other ISL links with a pending standby request (e.g., ISL link 126). If switch 106 determines that it cannot place ISL link 124 in standby mode in addition to placing ISL link 126 in standby, switch 130 will reject the standby request for ISL link 124.

FIG. 3 presents a flow chart illustrating a method 300 for processing a standby request from a neighboring cluster in accordance with an embodiment. During operation, the HSL module can determine whether it has received a new standby request from a neighbor of the switch network (operation 302). If no standby requests arrive, the HSL module can return to operation 302 to wait for a standby request.

When the HSL module does receive a standby request from a neighbor, the HSL module determines whether there are any pending standby requests from any of the local line cards (operation 304). If there are requests pending from at least one local line card, the HSL module can return to operation 304 to wait for these local pending standby requests to be processed.

Once the HSL module determines that there are no local pending standby requests, the HSL module proceeds to determine whether the eligible ISL links can accommodate traffic from the links associated with the new standby request (operation 306). If the eligible links cannot accommodate the traffic, the HSL module discards the new standby request (operation 308).

However, if the traffic can be accommodated over the eligible ISL links, the HSL module determines whether the QoS priority level of the eligible ISL links is sufficiently high to satisfy the QoS priority requirements of the ISL links associated with the pending standby requests (operation 310). If the QoS priority level is not sufficiently high, the HSL module discards the new standby request (operation 308). Otherwise, the HSL module may proceed to place the ISL link associated with the new standby request in standby mode (operation 312).

FIG. 4 illustrates an exemplary switch network 400 after placing links 410 and 418 in standby mode in accordance with an embodiment. Recall that a line card for each ISL link can have a transmission (tx) circuit and a receiving (rx) circuit, and two line cards at opposing ends of an ISL link may place the ISL link in standby mode when the transmission rate drops below the minimum threshold for both directions. If switch 402 sends to switch 404 a standby request to deactivate ISL link 418, switch 404 may reject the standby request message from switch 402 when switch 404 itself needs to transmit packets over ISL link 418.

As a further example, switch 404 may reject a standby request from switch 402 when switches 402 and 404 each issues a standby request for a different ISL link of ISL trunk 408, and there would not be sufficient bandwidth after disabling the two different ISL links. If switch 404 issues a standby request for ISL link 404 and receives a standby request for ISL link 418, Switch 404 may reject the incoming standby request for ISL link 418 if the bidirectional bandwidth across ISL trunk 408 is too large for ISL link 416 alone. However, if switch 404 issues a standby request for ISL link 418 and also receives a standby request for ISL 418 from switch 402, switch 404 may return an acknowledgement message to disable ISL link 418 since both switches 402 and 404 are in agreement.

Once both ISL links 402 and 404 agree to deactivate ISL link 418, the corresponding line cards at switches 402 and 404 will turn off their tx and rx circuits to preserve power. Also, switches 402 and 404 will update the TKSM for trunk 408 to remove ISL link 418 from trunk 408.

In some embodiments, a switch can place multiple ISL links in standby mode at once. For example, the network traffic across ISL trunk 408 may drop to a low enough bandwidth to place two out of three ISL links in standby mode. Switch 402 may analyze priority values associated with the individual ISL links of trunk 408 to decide which ISL links to place in standby mode. Switch 402 may disable the ISL links with the lowest priority first, to allow the ISL links with higher priority to remain active.

As a further example, there may exist two trunks between switch 404 and a switch 406: trunk 410 and trunk 412. If the traffic for trunk 412 drops below a minimum threshold, switch 404 may analyze trunk 410 to determine whether ISL trunk 410 can carry the traffic of ISL trunk 412. If so, switch 404 can issue a standby request message to switch 406 to disable a complete trunk (e.g., to disable ISL trunk 412, made up of links 424 and 426).

Activating a Standby ISL Link or Trunk

In some embodiments, switch 402 can activate a standby ISL link 418 when bandwidth across ISL trunk 408 increases above a maximum threshold. For example, if a HSL software module for ISL link 414 or ISL link 416 detects that the link's bandwidth is above the maximum bandwidth threshold, the HSL software module issues an activate request message to switch 402. Switch 402 processes the activate request by determining which other ISL links can be activated to offload some of the bandwidth from the overloaded ISL links. Since ISL link 418 is in standby mode, switch 402 can respond to the activate request by activating ISL link 418, and distributing the traffic for ISL trunk 13 across ISL link 418 in addition to links 414 and 416.

In some embodiments, switch 402 can activate ISL link 418 without requiring switch 120 to send an activation request message to switch 404, and without requiring switch 404 to return an activation acknowledgement message. Recall that switches 402 and 404 can place ISL link 418 in standby mode by each deactivating a transmitter and receiver on a line card for ISL link 418. When switch 402 activates ISL link 418, the line card for ISL link 418 at switch 402 can initiate a physical layer link bring-up routine that activates ISL link 418, without having to wait for switches 402 and 404 to first agree on activating ISL link 418.

FIG. 5 presents a flow chart illustrating a method 500 for processing a link activate request to activate a link in standby mode in accordance with an embodiment. During operation, the switch can determine whether it has received a link activate request from a line card (operation 502). If the switch has not received a link activate request, the switch can return to operation 502 to wait for a link activate request. Once the switch receives a link activate request from a line card, the switch determines whether any standby ISL links exist (operation 504). If no ISL links are currently in standby mode, the switch may discard the activate link request (operation 506), or may perform another remedial action. Some exemplary remedial actions include storing the ignored link activate request in a log file.

However, if at least one ISL link is in standby mode and eligible to be activated, the switch can select a standby link among the eligible standby links, for example, based on their QoS parameters (operation 508). In some embodiments, the switch selects a standby ISL link that has a lowest QoS priority among the set of eligible ISL links in standby. The switch then activates the selected link (operation 510), and can inform one or more software modules of the ISL link's active status (operation 512).

In some embodiments, when the switch activates the standby ISL link, the switch also updates a link state machine that keeps track of the ISL links that are currently available at the local switch.

Also, when the switch activates the ISL link, a local line card that corresponds to this ISL link will perform a physical-layer bring-up routine that communicates with a remote line card at the other side of the ISL link to transition the ISL link from standby mode to active mode. The local switch module does not need to send an activate message to a switch at the other side of the ISL link. Once the ISL link is active, the local switch and the remote switch individually update their trunk state machine (TKSM) to add the new ISL link to a trunk associated with the requesting ISL link.

FIG. 6 illustrates an exemplary member switch of a switching network, in accordance with one embodiment of the present invention. In some embodiments, switch 600 can be running special switch fabric software. Switch 600 includes a number of Ethernet communication ports 601, which can transmit and receive Ethernet frames and/or TRILL encapsulated frames. Also included in switch 600 is a packet processor 602, a virtual switch management module 604, a logical switch 605, a switch fabric configuration database 606, and a header generation module 608.

During operation, packet processor 602 extracts the source and destination MAC addresses of incoming frames, and attaches proper Ethernet or TRILL headers to outgoing frames. Virtual switch management module 604 maintains the state of logical switch 605, which is used to join other fabric switches using the switch fabric protocols. Fabric configuration database 606 maintains the configuration state of every switch within the switch fabric. Header generation module 608 is responsible for generating proper headers for frames that are to be transmitted to other switch fabric member switches. During operation, packet processor 602, virtual switch management module 604, fabric configuration database 606, and header generation module 608 jointly perform the methods described herein.

The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer-readable media now known or later developed.

The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium.

Furthermore, the methods and processes described above can be included in hardware modules. For example, the hardware modules can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules.

The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims. 

What is claimed is:
 1. A switch, comprising: one or more line cards; and power control circuitry coupled to the one or more line cards and configured to: identify a first standby request for placing a first link in a standby mode; determine whether at least one eligible link can accommodate traffic from the first link; and place a local line card corresponding to the first link in standby mode in response to the at least one eligible link being able to accommodate traffic from the first link.
 2. The switch of claim 1, wherein the eligible link does not have a corresponding pending standby request.
 3. The switch of claim 1, wherein the power control circuitry is further configured to reject the first standby request responsive to determining that there are insufficient number of eligible links to accommodate traffic from the first link.
 4. The switch of claim 1, wherein the first standby request is originated from the local line card, and wherein the power control circuitry is further configured to: generate a second standby request for placing the first link in standby mode, the second standby request being destined to a neighboring switch corresponding to the first link; and reject the first standby request in response to absence of acknowledgement to the second standby request within a timeout period.
 5. The switch of claim 1, wherein the power control circuitry is further configured to: identify another pending standby request for a second link; determine that there are insufficient number of eligible links to accommodate traffic from the first link and the second link; and reject the first standby request.
 6. The switch of claim 1, wherein the first standby request is originated from a neighboring switch, and wherein the power control circuitry is further configured to: determine whether there exists a pending local standby request for the first link; and responsive to determining that a pending local standby request exists, defer processing the first standby request.
 7. The switch of claim 1, wherein the power control circuitry is further configured to: determine whether a priority associated with the at least one eligible link is sufficiently high to accommodate traffic from the first link; and reject the first standby request responsive to determining that the priority associated with the at least one eligible link is not sufficiently high.
 8. The switch of claim 1, wherein the power control circuitry is further configured to: responsive to placing the first link in standby mode, determine whether the first link is a member of a trunk; and responsive to determining that the first link is a member of the trunk, update trunk state information to remove the first link from the trunk.
 9. The switch of claim 1, wherein the power control circuitry is further configured to: identify a link activate request; select, from a set of eligible links in standby mode, a link with a lowest priority that satisfies a priority requirement associated with the link activate request; and activate the selected link.
 10. A method, comprising: identifying a first standby request for placing a first link in a standby mode; determining whether at least one eligible link can accommodate traffic from the first link; and placing a local line card corresponding to the first link in standby mode in response to the at least one eligible link being able to accommodate traffic from the first link.
 11. The method of claim 10, wherein the eligible link does not have a corresponding pending standby request.
 12. The method of claim 10, further comprising rejecting the first standby request responsive to determining that there are insufficient number of eligible links to accommodate traffic from the first link.
 13. The method of claim 10, wherein the first standby request is originated from the local line card, and wherein the method further comprises: generating a second standby request for placing the first link in standby mode, the second standby request being destined to a neighboring switch corresponding to the first link; and rejecting the first standby request in response to absence of acknowledgement to the second standby request within a timeout period.
 14. The method of claim 10, further comprising: identifying another pending standby request for a second link; determining that there are insufficient number of eligible links to accommodate traffic from the first link and the second link; and rejecting the first standby request.
 15. The method of claim 10, wherein the first standby request is originated from a neighboring switch, and wherein the method further comprises: determining whether there exists a pending local standby request for the first link; and responsive to determining that a pending local standby request exists, deferring processing the first standby request.
 16. The method of claim 10, further comprising: determining whether a priority associated with the at least one eligible link is sufficiently high to accommodate traffic from the first link; and rejecting the first standby request responsive to determining that the priority associated with the at least one eligible link is not sufficiently high.
 17. The method of claim 10, further comprising: responsive to placing the first link in standby mode, determining whether the first link is a member of a trunk; and responsive to determining that the first link is a member of the trunk, updating trunk state information to remove the first link from the trunk.
 18. The method of claim 10, further comprising: identifying a link activate request; selecting, from a set of eligible links in standby mode, a link with a lowest priority that satisfies a priority requirement associated with the link activate request; and activating the selected link.
 19. A computer system, comprising: a processor; a storage device coupled to the processor and storing instructions which when executed by the processor cause the processor to perform a method, the method comprising: identifying a first standby request for placing a first link in a standby mode; determining whether at least one eligible link can accommodate traffic from the first link; and placing a local line card corresponding to the first link in standby mode in response to the at least one eligible link being able to accommodate traffic from the first link.
 20. The computer system of claim 19, wherein the method further comprises rejecting the first standby request responsive to determining that there are insufficient number of eligible links to accommodate traffic from the first link. 